1. Field of the Invention
This invention relates to spatial light modulators, more particularly to their memory and timing requirements.
2. Background of the Invention
The use of spatial light modulators results in desirable gains in speed, cost and control in systems used in fields such as printing, and high definition television. A spatial light modulator normally consists of an array of cells, preferably individually controllable. Each cell has an electrode or some sort of addressing node that allows that cell to be turned OFF and ON. Typically, a cell that is ON directs the light towards a surface, either through transmission or reflection. In this manner, each dot on a resultant picture, print surface, or even film, can be controlled by the system users.
A problem exists in the data and time requirement for such an array. In high definition television, for example, an array of pixels 2048 wide by 1024 long would not be unusual. Such an array of pixels would require over 2 million data points to be transferred every time the array was updated with new information. In order for the image to be produced from a single array to be in color, a typical 3-color scheme of red, green, and blue would require that the array be updated three times for every frame of information.
To illustrate this point, assume that one-third (one color) of a frame is 5.56 milliseconds (5.56.times.10.sup.3 seconds). The steady-state data rate for 2 million pixels with 8 bits of each color would then be (2,000,000.times.8)/0.00556 which equals approximately 2.8.times.10.sup.9, or 2.8 Gigahertz. The burst data rate, which is the highest rate at which data would be delivered to the modulator, takes into account the frame refresh rate for the pixel array. The fastest framing modulator is probably the digital micromirror device (DMD), which offers the worst-case scenario for update times. Assuming a 60 .mu.second refresh rate for this device, the burst data rate is 2,000,000/0.00006, equaling 30 Gigahertz.
The problem with these data rates comes at the transfer of data. To handle a 30 Gigahertz data rate with a reasonable signal transmission speed, 25 Megahertz, for example, the resulting number of wires is 30.times.10.sup.9 /25.times.10.sup.6, or 1200 wires. Transmitting data along 1200 wires from a remote processor to a spatial light modulator would be inefficient and costly. Obviously, a way to eliminate this problem is desired.